“Do unto others as you would have them do unto you.” ... Even when talking to children, who says such things?

I recall telling kids such things as “How would you feel if someone did that to you?” which I hope you will agree have a similar effect, if they work at all.

But small kids are a bit like dogs—it’s the tone of voice and the body language more than the words that do the work. Then it’s the effect of the quoted sentiment on one’s own peace of mind that helps.

Similarly with good philosophy—the effect on one’s own mind is often more important than whether one can get some wise-guy idiot to agree.